First you have to know what the insolation potential is in your area. This is the amount of available sunlight energy that arrives at the Earth’s surface per area (square meter.) Latitude and cloud cover (humidity) are influential factors.1 Arizona has higher average insolation levels than Maine.

Next you would need to know the efficiency levels of your particular brand of solar photovoltaic panels. They are typically between 8 and 22%. Here are some samples: 2 You will require more panels if they are less efficient. The price should be lower for panels that are less efficient but the only way to determine value would be to table or graph the results and determine totals. A spreadsheet will help.

Last you need to add the output to get at least 110% of the desired result. You can expect that an inverter will take cost you 10% of the output.

Even better than the average cost of a panel would be the average cost of an installed system. But since you asked about the panels you can use the list under (2) to look up prices. Prices are always changing and there are always deals to be made.